﻿using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;
using System.Threading.Tasks;

namespace Utils
{
    public class RC2Helper
    {
        /// <summary>
        /// RC2 加密(用变长密钥对大量数据进行加密)
        /// </summary>
        /// <param name="EncryptString">待加密密文</param>
        /// <param name="EncryptKey">加密密钥(密钥长度为5~16位)</param>
        /// <returns>returns</returns>
        public string Encrypt(string EncryptString, string EncryptKey)
        {
            if (string.IsNullOrEmpty(EncryptString)) { throw (new Exception("密文不得为空")); }

            if (string.IsNullOrEmpty(EncryptKey)) { throw (new Exception("密钥不得为空")); }

            if (EncryptKey.Length < 5 || EncryptKey.Length > 16) { throw (new Exception("密钥必须为5-16位")); }

            string m_strEncrypt = "";

            byte[] m_btIV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

            RC2CryptoServiceProvider m_RC2Provider = new RC2CryptoServiceProvider();

            try
            {
#if Standard
            System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);
#endif
                byte[] m_btEncryptString = Encoding.Default.GetBytes(EncryptString);

                MemoryStream m_stream = new MemoryStream();

                CryptoStream m_cstream = new CryptoStream(m_stream, m_RC2Provider.CreateEncryptor(Encoding.Default.GetBytes(EncryptKey), m_btIV), CryptoStreamMode.Write);

                m_cstream.Write(m_btEncryptString, 0, m_btEncryptString.Length);

                m_cstream.FlushFinalBlock();

                m_strEncrypt = Convert.ToBase64String(m_stream.ToArray());

                m_stream.Close(); m_stream.Dispose();

                m_cstream.Close(); m_cstream.Dispose();
            }
            catch (IOException ex) { throw ex; }
            catch (CryptographicException ex) { throw ex; }
            catch (ArgumentException ex) { throw ex; }
            catch (Exception ex) { throw ex; }
            finally { m_RC2Provider.Clear(); }

            return m_strEncrypt;
        }
        /// <summary>
        /// RC2 解密(用变长密钥对大量数据进行加密)
        /// </summary>
        /// <param name="DecryptString">待解密密文</param>
        /// <param name="DecryptKey">解密密钥(密钥长度为5~16位)</param>
        /// <returns>returns</returns>
        public string Decrypt(string DecryptString, string DecryptKey)
        {
            if (string.IsNullOrEmpty(DecryptString)) { throw (new Exception("密文不得为空")); }

            if (string.IsNullOrEmpty(DecryptKey)) { throw (new Exception("密钥不得为空")); }

            if (DecryptKey.Length < 5 || DecryptKey.Length > 16) { throw (new Exception("密钥必须为5-16位")); }

            byte[] m_btIV = { 0x12, 0x34, 0x56, 0x78, 0x90, 0xAB, 0xCD, 0xEF };

            string m_strDecrypt = "";

            RC2CryptoServiceProvider m_RC2Provider = new RC2CryptoServiceProvider();

            try
            {
#if Standard
            System.Text.Encoding.RegisterProvider(System.Text.CodePagesEncodingProvider.Instance);
#endif
                byte[] m_btDecryptString = Convert.FromBase64String(DecryptString);

                MemoryStream m_stream = new MemoryStream();

                CryptoStream m_cstream = new CryptoStream(m_stream, m_RC2Provider.CreateDecryptor(Encoding.Default.GetBytes(DecryptKey), m_btIV), CryptoStreamMode.Write);

                m_cstream.Write(m_btDecryptString, 0, m_btDecryptString.Length);

                m_cstream.FlushFinalBlock();

                m_strDecrypt = Encoding.Default.GetString(m_stream.ToArray());

                m_stream.Close(); m_stream.Dispose();

                m_cstream.Close(); m_cstream.Dispose();
            }
            catch (IOException ex) { throw ex; }
            catch (CryptographicException ex) { throw ex; }
            catch (ArgumentException ex) { throw ex; }
            catch (Exception ex) { throw ex; }
            finally { m_RC2Provider.Clear(); }
            return m_strDecrypt;
        }
    }

}
